Hot-air furnace



P 1944. R. L. JUDY 2,357,831

HOT AIR FURNACE Filed May 19,- 1941 Gttornegs Patented Sept. 12, 1944UNITED STATES PATENT. OFFICE HOT-AIR FURNACE Ralph L. Judy, nearKirkland, Wash.; Myrtle M. Judy executrix of said Ralph L. Judy,deceased Application May 19, 1941, Serial No. 394,177

4 Claims.

My invention relates to a novel furnace construction, particularly -welladapted for incorporation in domestic heating furnaces of the hot airtype, and is equally advantageous where air conditioning equipment isemployed in the system.

In most furnaces for use in home heating, which heat air to berecirculated through the house, the heating efficiency of theconstruction employed is quite low. Various expedients have been triedfor increasing the efficiency of such installations with greater or lesssuccess, but in most cases it was found that where the cost of theconstruction was not prohibitive from a commercial standpoint only avery small increase in efficiency was obtained.

Further diificulties were also experienced in such structures in thatcertain parts would tend to become overheated and burn out quiterapidly, and the structures providing an intricate maze of heat transferpassages were very difficult to clean or repair, as Well as beingexpensive to construct. As a result, a high efficiency hot air heatingplant for domestic use has not been available at a reasonable cost.

In general my construction includes a furnace casing having a combustionchamber in its lower portion which is fired preferably by an oil burnerof the pressure atomizing or injection type, although other fuels andburner types may be used instead as the heat source. Above thiscombustion chamber are arranged two sections of generally horizontalheating tubes, interconnected by headers so that the hot combustiongases pass from the combustion chamber to the lower set of radiatingtubes in one horizontal direction, and then in the opposite directionthrough the upper set of heat radiating tubes, to pass out the flue.

The air to be heated for recirculation through the house enters thelower portion of the side of the furnace casing immediately above thecombustion chamber and in the zone occupied by the lower set of heatingtubes. The entering air is thus warmed by heat radiated both from theroof of the combustion chamber proper and from the heating tubesthemselves. The air, after passing generally horizontally about thelower set of heating tubes, flows upward into the chamber housing theupper set of heating tubes, about which it also passes in a generallyhorizontal, but opposite, direction, and then passes out through the airdischarge outlet from the furnace casing. Thus both the combustion gasesand the air to be heated pass upward through the furnace caspreferablydisposed mutually transversely, and intersect each other.

Damper mechanism is provided to regulate the flow of combustion gases sothat the volume of such flow will be approximately equally distrib utedthrough all the heat radiating tubes of each set. All the tubes,therefore, can operate with the same efficiency.

The principal object of my invention is to provide a furnace of simpleand inexpensive construction which nevertheless will afford unusuallygreat efficiency, and to provide such a construc tion which will besuitable for use in furnaces burning any of the customary types of fuel.Such general object is primarily to be accomplished by greatlyincreasing the heat radiating surface within the furnace casing by asimplified heat exchange construction, and constraining movement of theair to be heated to intimate contact with such extensive heat radiatingsurface.

Another object is to provide such a construction which will be readilyaccessible for cleaning of the parts which might tend to accumulatesoot, and it is also an object to provide proper damp ers or equivalentcontrol means for equalizing the flow over the heat-radiating surfaces,thus to discourage deposit of soot on them, as well as to increasegenerally the heat transferring efficiency of the furnace byequalizingthe temperature differential between the combustion gases andthe air to be heated throughout each of the several heating zones. 7

Still a further object is to provide a construction in which the air tobe heated, as well as the combustion gases, will traverse a tortuouspath between and aroundthe heat-radiating surfaces in such a manner thateach portion of the air flow will travel approximately the same distancein its circuit as the other portions of the air flow, thus tending toequalize distribution of the heat absorptive medium, and to obtainsubstantially uniform flow velocity throughout such passage. It isintended, however, that the airconnections be such that an airconditioning system can be employed conveniently in conjunction with thefurnace. V

Other objects of my invention and important characteristics of theconstruction and operation of my furnace will be presented in thefollowing specific description of the representative furnaceconstruction illustrated in the drawing.

Figure 1 is a. vertical longitudinal section through the furnace, takenalong line l-l of Figure 2, while Figure 2 is a vertical transversesecing in Shi -91 pentine p ths, which are tion along line 2-2 ofFigure 1. i

Figure 3 is an end elevation view of the upper portion of the furnace,showing part of the casing broken away to expose the internal furnacestructure.

Figure 4 is a fragmentary side elevation view to an enlarged scale,showing damper-operating mechanism.

In general the furnace consists of a casing I 7 within which is locateda generally horizontal partition ID forming the roof of the combustionchamber As previously mentioned, any of the customary fuels can be usedfor heating in my furnace, but I believe that the best results can beobtained by the use of oil, and consequently I have illustrated thepressure atomizing or injection type of oil burner I I, which projectsinto the combustion chamber through an aperture I2 in the front of thefurnace casing Preferably the partition ID terminates forwardly or shortof the back wall of the furnace casing I, as shown in Figure 1, leavingan upwardly extending shaft or cavity defined by a generally verticalforward wall I3 and by anupright rearward wall I4, which may be inclinedor curved rearward and downward in the manner shown. The top of thiscavity is closed by qne'er d of a second horizontal partition I5, whichwill be described more fully later, to form, with the portion of thecasing beneath partition 10, a generally L-shaped combustion chamberwith a horizontal leg and an upright leg. In order to enable thecombustion chamber to be cleaned'out readily an aperture I6, closed by adoor I'I, may be provided in therear wall of the casing I. Such. aclean-out door "may be hinged, or otherwise supported in any suitable Imanner.

Above the combustion chamber are located two additional p eltitions, onea vertical partition 2 near the front wall of the casing I, andextending upward from the lowest horizontal partition I0, and the otheranother horizontal partition 2|] above I and located near the top wallof the casing. These two partitions meet near the top front edge of thefurnace, and partition I5 is joined to the central portion of partition2. Partition |4 extends upward from its junction with partition I5substantially parallel topartitions 2 and I3, and is also joined topartition 20; Preferably the portion of partition I4 above partition I5is spaced approximately the same distance from the back wall of thecasing I as partition 2 is spaced from the front casing wall.

Extending generally horizontally between up-.- right partitions 2 and I3 and substantially equally spaced from each other and from partitionsIOand I5 are horizontal heating tubes 2| which communicate both with theupright leg of the generally L-shaped combustion space in the lowerportion of the casing and. with the front header or manifoldchamberbetween the front wall of casing and partition 2. The inclinedportion of wall I4 serves to deflect the combustion gases from suchupright leg into the enter? ing end of these tubes. A similar butslightly longer set of tubes 22 extends between the; upper portions ofpartitions 2 and I4, the tubes being approximately equally spaced fromeach other and-from the horizontal partitions l5 and 20. It will beevident that the number of tubes 2| and 22 in each set may be varied, ascan the size and wall thickness of each tube, the selectionof thesefactors depending upon the type of fuel being burned,the heatingcapacity'of the furnace, the length of the tubesQth'eir relativespacing, and other considerations which may be involved in determiningthe best design for particular installations and operating requirements.

A flue 23 is connectedto the rear header or manifold chamber betweenpartition I4 and the rear wall of the furnace, while immediately belowthe flue connection a second clean-out aperture 24 is provided, normallyclosed by a door 25, affording access to this header space for cleaningpurposes, to be described more fully hereafter. The flow of through thisheader to the flue may be controlled by a damper 26 journled on a rod21. Any suitable means can be employed for swinging and holding thisdamper in the setting to afford the desired operation. Such means mayconven-' iently be an arm 28 secured by one end to rod 21 and having itsother end apertured for con-' nection to an arcuate plate 29 by a pininserted through it and into the appropriate one of the e a h le r uplate,v t reta n damp in the proper swung position. V

And to be heated for recirculation through the dwelling is suppliedthrough a conduit 3 connected to the side of the furnace casing, inwhich ma e p de p e ans, f rs, a humidifying equipment to condition theair before it is heated. The air thus admitted takes the sinuous upwardcourse transversely ofthe furnace casing indicated by the arrowsinFigure 2, being discharged through, opening 30, The portion of partitionI5 between wall I3 and wall I4 extends completely from side to side ofthe furnace casing, so that no combustion gases are admitted to the airspace but all are compelled to flow through tubes 2| inthe directionindicated by the arrows in Figure 1 for exit from tend completely fromside to side of the casing, 1

and only betweenpartitions 2 and I4 in a space left between an edge ofpartition 20 and a side wall of the furnace casing through which air maypass to the outlet .3

In Orderthat'sootmay be removed readily from tubes 2| and 22 clean-outapertures I8, one registering with each tume, are provided in the frontwall of the furnace casing 'I, each covered by an individual plate I9,removably'secured in place by screws or equivalent means; Instead ofproviding a separate aperture for each tube it will be evident thatasection of the front casing Wall between partitions I0 and, 20 and of awidth suflicient to expose the, ends of. all the heat-radiating tubesmight be made removable.

A suitable cleaning brush can then be pushed through each tube from itsend projecting through partition 2 the soot from tubes 2| being pushedrearwardly .downi-nto the combuscombustion gases The efificient heatexchange capabilities of my furnace will be readily recognized. Thecombustion gases give up heat to the air entering intake 3 through theroof III of the combustion chamber itself. They then pass upward to thefiue outlet in a sinuous or serpentine path of generally S-shape, firstinto the cavity between walls I3 and I4 forming the upright leg of theL-shaped combustion chamber. Here an additional amount of heat isradiated to the air through the wall '13 and the roof I5 before thegases pass horizontally into the tubes 2l.- Next heat is radiated fromthem through the tube walls to the air flowing about the tubes until thecombustion gases pass into the forward header. As they again rise heatis radiated through wall 2 and the roof 20 of this compartment until thecombustion gases pass again horizontally but in the opposite directioninto the upper set of tubes 22. Through their walls heat is radiated toair circulating'about these tubes until the gases pass into the rearheader. From this chamber the final remainder of heat which can beeffectively removed from the combustion gases is transmitted to the airthrough the roof portion formed by part of partition 26 and through theupper part of Wall M, because the combustion gases now must movedownward for discharge into flue 23. The sinuous path traversed by thecombustion gases is therefore such that they come into intimate contactwith a very large amount of heat absorbing surface.

Not only are such surfaces arranged so that heat can be picked up bythem readily from the combustion gases, but the airflow on theiropposite sides is such that the heat radiated by them can be removed bythe air to best advantage. Thus the coldest air will pass generallyhorizontally into the side of the furnace casing through the lowerportion of duct 3 ,and immediately across the roof ll] of the combustionchamber, so that a maximum amount of heat can be transmitted to itduring such travel and such roof will simultaneously be prevented fromover heating.

The air thus warmed will pass around and over the surfaces of tubes 2|.While these have been shown in registry they may be arranged instaggered relationship to increase the turbulence and deviation of airflow, if desired. Ordinarily, however, this is unnecessary, and mighttend to create excessive resistance to passage of air through thefurnace.

From the heating zone of pipes 2| the air will pass upward around theedge of partition [5 as shown in Figure 2 into the heatin zone of pipes22, where it will flow generally in the opposite horizontal directionabout and over the surfaces of these pipes. The air then flow upwardaround the edge of partition 20 for exit through duct 30. During itstransit through the furnace, therefore, from duct 3 to duct 30 the airhas traversed an S shaped path, so that the air on the inside of onecurve of such path will be on the outside of the next curve, and viceversa, causing the column of air to move with substantially uniformaverage velocity in all its parts. At the time of its passage throughthe tube chambers the air will also, of course, pick up a certain amountof heat radiated from the end walls l3, I4, and 2, as well as from theportions of horizontal partitions I5 and 20 previously mentioned. In thelatter case the heat will be conducted toward the center of thesepartitions for better distribution of the heat to the air.

sinuous, generally S-shaped path crosswise 'of the furnace mentionedabove, the combustion gases will move through a sinuous, generally 8-shaped path lengthwise of the furnace, as previously described, composedof the combustion chamber, the cavity at the back of the furnace, tubes2|, the header cavity at the front of the fur.- nace, and tubes 22.These two paths will thus be disposed in mutually transverse,intersecting relationship.

Depending on the proportions of th various parts, as well as on theirrelationship to each other, it is probable that the flow through theupper and lower rows of tubes 22 will not be equal. In order to maintainas far as possible a uniform temperature differential between all thetubes 22 and the air in that chamber, and in order to reduce thetemperature of all portions of the air entering flue 23 to the samevalue, I provide the damper 26, which may be adjusted from the verticalor even from a rearwardly swung position into the forwardly swungposition shown in broken lines in Figure 1. The holes provided onthe'curved plate 29, shown in Figure 4, will enable the damper operatingarm 28 to be set in any selected one of a large number of positions, sothat the angularity of damper 26 in the header chamber at the rear ofthe furnace may be adjusted with accuracy and maintained in suchadjusted position. Under ordinary conditions it will probably benecessary to swing the damper plate slightly forward on its hinge rod 21so that a freer flow will be provided through the slightly longer pathof the upper row of tubes 22 than through the lower row. As a result thevelocity and quantity of combustion gas flowing through each tube 22should be equal to that flowing through each other such tube. It will beunderstood that conventional draft doors and dampers will be provided asusual in addition to damper 26 for controllin the combustion within thecombustion chamber.

What I claim as my invention is:

1. In a heating furnace, a casing defining a combustion chamber in thelower portion thereof, a lower group of generally horizontal heatingtubes extending lengthwise within said casing and having one endcommunicating with the'combustion chamber, an upper group of generallyhorizontal heating tubes extending lengthwise within said casing, meansinterconnecting the other end of said lower group of tubes with one endof said upper group of tubes, a flue communieating with the other end ofsaid upper group of tubes, both said upper and lower groups of tubesbeing spaced a substantial distance from both side walls of said casing,a generally horizontal baffle plate between said upper and lower groupsof heating tubes, spaced a substantial distance from While the air to betreated is traversing the both tube groups, projecting from a side wallof said casing. across the entire width and length of said lower groupof tubes and having a free edge spaced from the opposite side wall ofsaid casing to leave a passage therebetween, an air inlet duct connectedto the side of said casing from which said baflle plate projects andbetween said Plate and the combustion chamber for directing air to beheated generally horizontally transversely across the outer surfaces ofthe heating tubes in said lower group, and upward past the free edge ofsaid baffle plate, means below the top of the casing and spaced asubstantial distance above the upper group of tubes, guiding such airfor flow thence transversely acros the outer surfaces of the heatingtubes in said upper group, and an air 'outlet ductconnected to the upperpart of said casing for receiving the air heated during; such passage.

necting the other end of said lower group of tubes with one end of saidupper group of tubes,

a flue communicating with the other end of said upper group oftubes,both said upper and lower groups :of tubes being spaced atsiibstantialdistance from both side Walls of said casing, an uppergenerally horizontal baflle plate above said upper group of tubes,projecting from one side wall-of said casing across the entire width andlength of said upper group of tubes and having a free edge spaced fromthe opposite side wall of said casing to leave a passage therebetween, alower generally horizontal bafile plate between said upper and lowergroups of heating tubes, projecting from the side wall of said casingopposite that from which said upper baffle plate projects across theentire width and length of said lower group of tubes, and having a freeedge spaced from the casing side wall opposite that from which itprojects to leave a passage therebetween, an air inlet duct connected tothe side of said casing from which said lower baffle plate projectsbetween it and the combustion chamber, for directing air to be heatedgenerally horizontally transversely across the outer surfaces of theheating tubes in said lower group, then upward past the free edge ofsaid lowerbaille plate, then transversely across the outer surfaces ofthe heating'tubes' in said upper group, and then upward past the freeedge of said upper bafile plate, and an air outlet duct connected tosaid casing above said upper 'bafile plate for receiving the air heatedduring such passage,

3. In a heating furnace, a casing defining a combustion chamber in thelower portion thereof, a lower group of generally horizontal heatingtubes extending lengthwise within said casing and having one endcommunicating with the combustion chamber, an upper group of generallyhorizontal heating tubes extending lengthwise Within said casing, acommon header interconnecting the other end of said lower group of bothsaid upper and lower groups of tubes being spaced a substantial distancefrom both side walls of said casing, an upper generally horizontal'baflie plate above said upper group of tubes, projecting from one sidewall of said casing across the entire width and length of said uppergroupof tubes and having a freeedge ass-7,831

the entire Width and length of said lower group of tubes, and having afree edge spaced from the casing side wall opposite that from which itprojects to leave a passage therebetween, an air inlet duct connected tothe side of said casing from which said lower baffle plate projectsbetween it and the combustion chamber, for directing air to be heatedgenerally horizontally transversely across the outer surfaces of theheating tubes in said lower group, then upward past the free edge ofsaid lower baflie plate, then transversely across the outer surfaces ofthe heating tubes in said upper group, and then upward past the freeedge of said upper bafile plate, an'air outlet duct connected to saidcasing above said upper baflle plate for receiving the air heatedincludingan upper row and a lower row extending lengthwise within saidcasing and having one end communicating with the combustion chamber, aflue header having the other end of i said group of tubes connected toone side thereof, an air inlet duct connected to a side of said casingfor admission of air to be heated, means within said casing guidingsuchair forflow transversely across the outer surfaces of all the heatingtubes in'said group, an air outlet duct connected to the upper part ofsaid casing for receiving air thus heated, a flue connected to the sideof said flue header opposite that to which said group of tubes isconnected, and at a location below such connection of the lower row ofheating tubes in said group, a horizontal pivot rod journaled in saidflue header substantially midway between the header sides towhich saidtubes and said flue are connected, andat a level substantially midwaybetween said upper and lower rows of heating tubes in said group, and aflow equalizing damper depending from said pivot rod,'inoperative tostop. flow through any of said tubes, but. swingalble by said rod tovary the relative cross-sectional area of the paths across saidflue'header from said upper row of heatingtubes and from said lower rowof heating tubes, respectively, to said flue.

RALPH L. JUDY.

